Safety switch device for electrically controlled machines

ABSTRACT

The invention relates to a safety switch unit ( 1 ) for electrically controlled machines for use in combination with the actual control elements of the machine control system in a hand-held application or for manual control, with at least one operating element which is displaced relative to a mounting frame ( 8 ) in accordance with the switching function desired by a user, which is designed to change the switch status of at least one electric switch element, the safety switch unit ( 1 ) having at least one switch position which is maintained only as long as a sufficiently high operating force is applied to the displaceable operating elements. Two operating elements for at least one respective electric switch element ( 14, 15 ) can be displaced in translation or rotation to a limited degree relative to the mounting frame ( 8 ) about a respective pivot axis of two pivot bearings and provide a substantially translating or straight operating movement of the safety switch unit ( 1 ) by means of a push button unit ( 2 ) which is disposed in front of the two operating elements by reference to the operating direction—arrow ( 13 )—of the safety switch unit ( 1 ).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of Austrian ApplicationNo. A1192/2001 filed on Jul. 31, 2001. Applicants also claim priorityunder 35 U.S.C. §365 of PCT/AT02/00215 filed on Jul. 19, 2002. Theinternational application under PCT article 21(2) was not published inEnglish.

The invention relates to a safety switch unit for electricallycontrolled machines, for use in combination with the actual controlelements of the machine control system in handheld applications or formanual control, as defined in claim 1.

Patent specification DE 199 09 968 A1 filed by the same applicantdescribes a safety switch unit for electrically controllable machines.This safety switch unit has several contact stages and two mutuallyindependent, redundant switch circuits. The active contact stages of thesafety switch unit are provided in the form of a key function, i.e. theycan only remain active as long as they are being actively depressed by auser. Detection systems which operate without contacts are provided as ameans of detecting the respective switch position and are connected toan electronic evaluation circuit. Two operating elements are used toswitch to the different contact states and are disposed so as to belinearly slidable relative to a housing in which they are partiallyenclosed. A linking arrangement or cap connecting the two operatingelements is provided, the purpose of which is to allow the operatingelements to be displaced simultaneously. It is also stated that thehousing has guide tracks designed so that the operating elements can beguided substantially without any clearance. As an alternative, it isalso pointed out that rotating motions can also be effected with theoperating elements in order to initiate the desired switching function.The specified construction requires relatively large integration depths,which means that this design is not suitable for all applications.Moreover, the more it is used, the more the arrangement proposed forguiding the linear or rotary motions of the operating elements is atrisk of mechanical jamming caused by dirt or abrasive wear on the slidesurfaces, for example. The guided sliding or rotating motions also needto be very precise, which increases the cost of producing the safetyswitch unit.

The underlying objective of the present invention is to propose a safetyswitch unit of high mechanical functioning reliability which can beoperated in the standard fashion.

This objective is achieved by the invention as a result of thecharacterising features defined in claim 1.

The advantage of this approach is that the safety switch unit is builtso as to incorporate two full circuits, including from a mechanicalpoint of view, and therefore meets the criteria of so-called fail-safecontrol. Another major factor is the specific way in which the operatingelements are mounted so as to pivot about pivot axes, which provides amechanically very reliable design that is guaranteed to functionperfectly and unimpaired irrespective of the number of operating cycles.In particular, the operating properties of the specified safety switchunit remain unaltered, even after numerous operating cycles, and it isnot susceptible to any significant wear. Also of particular advantage isthe fact that any risk of the operating elements sticking, moving out ofline or even jamming altogether is minimised due to the way in which theoperating elements are mounted so as to rotate about the correspondingpivot axes, thereby conforming to high safety requirements. The rotarymounting of the operating elements will not adversely effect the triggerbehaviour of the safety switch even if the operating force applied bythe user is off-centre, which means that it will be possible to outputthe respective switch commands correctly even in panic situations or ifthe safety switch unit is being held incorrectly or carelessly. The pushbutton unit nevertheless enables a substantially linear operating motionfor the safety switch unit to be achieved, thereby constituting thebasis for intuitive and familiar operation by the respective user.

As a result of the embodiment defined in claim 9, the points at whichforce is introduced into the push button unit are essentially fixed andare disposed above the switch elements, thereby enabling the force to betransmitted to the switch elements as directly as possible. In addition,this motion does not have to be reversed and instead the adjustmentdirection of the safety switch unit may be the same as the adjustingdirection for triggering switching procedures in the switch elements.

The embodiment defined in claim 11 offers a simple way of enablingspecial switching states of the safety switch unit to be detectedwithout the need for complex latching or locking mechanisms.

As a result of the embodiment defined in claim 14, switch elements thatare intrinsically relatively sensitive can be accommodated in aperfectly stable manner in a plastic housing and the switch elementswill still be very resistant to breakage and damage, even if theoperating force is applied quite forcefully, as would be the case inpanic situations, or if the correct operating mode were not used.

As a result of the embodiment defined in claim 17, in spite of therelatively large surface available on the push button unit for operatingpurposes, the safety switch unit is still relatively small in terms ofits construction size. In particular, the specified safety switch unitcan also be integrated in a device housing in which only a shallow depthis available for integration purposes.

The advantageous embodiment defined in claim 5 or 6 on the one handensures that the operating elements are mounted so that they will notbecome blocked or move out of line and on the other hand provides acentral zone at which force is introduced. Furthermore, the fact thatthe operating elements merge with one another within the zone in whichforce is introduced ensures that the operating elements will always becorrectly operated by the user even though the two operating elementsare mechanically independent or each mounted separately and notpositively coupled with one another in displacement.

With the embodiment defined in claim 21, the operating elements roll ina sliding arrangement relative to the push button unit when pivotedabout their pivot axes and the push button unit is supported on theoperating elements with as little friction as possible. In particular,an easy relative displacement is produced between the operating elementsand the push button unit disposed in front within the force transmissionzone, whilst inducing as little friction as possible

The embodiment defined in claim 24 ensures that the operating elements,which are mounted so that they move independently of one another, arealways moved simultaneously and conforming to the same shape whenoperating force is applied to the rubber-elastic cover element. Inaddition, the substantially dimensionally stable pressure-transmittingblock rules out the possibility of misalignment between the coverelement or push button unit and the pivoting operating elements.

As a result of the embodiment defined in claim 27, the safety switchunit can be switched from the contact stage constituting theconfirmation state to the contact stage representing panic mode withoutunacceptably high forces on the switching elements affecting thenormally open contacts. In addition, the requisite operating forces aresuch that they are perceptibly different because the resilientlyflexible compensating elements have to be deformed in order to switchfrom confirmation to panic mode.

The invention will be explained in more detail with reference toexamples of embodiments illustrated in the appended drawings.

Of these:

FIG. 1 is a simplified perspective diagram illustrating an embodiment ofthe safety switch unit;

FIG. 2 is a plan view of the safety switch unit illustrated in FIG. 1viewed in the direction of arrow II;

FIG. 3 is a simplified diagram of the safety switch unit illustrated inFIG. 2 in section along line III—III;

FIG. 4 is a perspective diagram showing individual parts of the safetyswitch unit illustrated in FIG. 1 with the mounting frame and apivotable operating element.

Firstly, it should be pointed out that the same parts described in thedifferent embodiments are denoted by the same reference numbers and thesame component names and the disclosures made throughout the descriptioncan be transposed in terms of meaning to same parts bearing the samereference numbers or same component names. Furthermore, the positionschosen for the purposes of the description, such as top, bottom, side,etc., relate to the drawing specifically being described and can betransposed in terms of meaning to a new position when another positionis being described.

FIGS. 1 to 4 are simplified partial diagrams illustrating an embodimentof the safety switch unit 1, intended to highlight the structure andoperating mode.

This safety switch unit 1 is preferably operated by a user who appliespressure with the finger. Naturally, however, it would also be possiblefor the safety switch unit 1 to be designed so that it can be operatedby the foot. The safety switch unit 1 is intended as a means ofcontrolling machines or robots in combination with the actual controlelements of the electric machine control system and, this being thecase, is specifically used to provide manual control of motion andfunction sequences of a machine. For example, the safety switch unit 1proposed by the invention is used during manual operation of amulti-axis robot arm or multi-axis processing machines, for example. Thesafety switch unit 1 is thus used in combination with the actual controlelements which have to be operated by the user, such as a controllerstick, a controller ball or a so-called “track ball”, directionalcontrol keys or similar for example, thereby enabling the machine undercontrol to perform a movement or function intended by the user only whenthe safety switch unit 1 is operated in a pre-defined manner. The safetyswitch unit 1 is therefore comparable to a confirmation system and canbe integrated in a stationary or mobile handheld control device for themachine or alternatively it can be used in conjunction with a switch orcontrol lever or similar.

The safety switch unit 1 is used for so-called “teach-in procedures” orlearning processes for robots, during which the motion sequence to beperformed by the robot arm is pre-set beforehand by means of a manualcontrol, after which the robot performs the motion sequence learnedduring the manual control process on its own.

The safety switch unit 1 is designed to operate on the basis of a pushbutton in particular, i.e. the switch position initiated by the user ismaintained only as long as the safety switch unit 1 is consciouslyoperated.

The safety switch unit 1 is therefore connected to at least some of theindividual control elements on a handheld device or control panel forthe respective machine so as to operate in what is virtually a serialmode. In other words, the machine will not perform the motion orfunction intended by the user unless the safety switch unit 1 is beingoperated in addition, preferably by the second hand of the user, therebyproviding confirmation of the motion or sequence to be performed. Thesafety switch unit 1 therefore fulfils a safety function since itensures that unintentional activation of the control elements for themachine or automated manipulator, caused by jostling for example, cannot cause uncontrolled movements or functions. Similarly, if a mobilehandheld device drops to the floor or is subjected to impact stress, nocritical control commands will be output unless the safety switch unit 1is simultaneously being operated in such a way that the confirmationmode is assumed.

The safety switch unit 1 may optionally also have a panic mode oremergency stop function, which can be initiated rapidly and reliably inthe event of a risk situation. In practice, since a hand or at least onefinger of the user is supported on the safety switch unit 1 whencritical motions or functions are being performed, only a shortadditional operating path has to be covered in order to ensure rapidswitching when necessary.

The specified safety switch unit 1 can reduce the risk of injury topersonnel on the one hand and minimise the risk of damage to machineparts or workpieces on the other, which all in all makes control of thecorresponding machine relatively safe. The construction of the safetyswitch unit 1 described below is very reliable both in terms ofmechanical and electrical operating functionality, so that these safetyaspects are always preserved.

In addition to an initial or inactive position, the safety switch unit 1has at least two switch positions and optionally also three differentswitch positions. In the first switch position or contact stage, inwhich the safety switch unit 1 is not being operated by the user, noconfirmation is given for a critical movement of a machine part or adangerous function of the machine being controlled and operated. Inorder to assume the second switch position or contact stage, the safetyswitch unit 1 must be operated, preferably by at least one finger of theuser, and only at this stage is the authorisation given for the machineto perform a helical movement or function, for example. Thisauthorisation or confirmation continues to apply only if the depressedposition of the safety switch unit 1 is maintained accordingly, inparticular is maintained only as long as a displaceably mounted pushbutton unit 2 (FIG. 3) of the safety switch unit 1 is actively depressedin the second contact stage. When the push button unit 2 is released, itimmediately returns to the initial or inactive position illustrated inFIGS. 1 and 3. In this initial or inactive position of the safety switchunit 1 or push button unit 2, therefore, the performance ofsafety-critical movements or functions is not authorised. The safetyswitch unit 1 is therefore designed as an automatic re-set button and,from a construction point of view, contains no mechanical locks orlatches to maintain its active switch positions or contact stages.

In the embodiment illustrated in FIGS. 1 to 4, the safety switch unit 1may be of a triple-action design, in which case the push button unit 2will not give authorisation for a critical movement or function of themachine to be performed when switched to the third or last switchposition and at this point in time any functions or movements of therespective machine which are safety protected and might have been activeare terminated immediately. This third contact stage is usuallytriggered by the user as a reflex reaction in the event of a panicsituation and as a rule is not intentional. For example, if there is arisk of injury to the user himself or any other persons in the areaaround the respective machine, this will usually be transmitted to thesafety switch unit 1 by a reflex reaction, so that the push button unit2 is moved via the second contact stage and beyond into the last orthird switch position. The same situation can arise if there is suddenlyan acute risk of the respective machine or the processed product beingdamaged. The “panic” or “emergency stop” switch mode on the safetyswitch unit 1, which may be optionally implemented and if necessarypermanently maintained and optionally actively re-set, is applied as aresult of appropriate precautions or features in the electric design ofthe safety switch unit 1 or the machine controller. In other words,there are no mechanical locks or latches for the third switch modetriggering the “panic mode” in the mechanics of the safety switch unit1.

A movement of a machine part or the performance of a function by amachine can not be authorised again until the push button unit 2 hasbeen fully released and the push button unit 2 operated again, startingfrom the inactive position and moving into the second contact stage. Asthe safety switch unit 1 is being re-set, in particular as the pushbutton unit 2 is switched from the third contact stage (panic) via theimmediately consecutive contact stage (authorisation) back to the firstcontact stage (inactive position), the safety switch unit 1 does notpermit any authorisation—not even briefly—so that there is no way inwhich the machine an be activated again—even briefly—if the push buttonunit 2 was previously in the third contact stage (panic) and thenreleased again. This so-called function lock or prevention of undesiredor critical switch or operating modes of the safety switch unit 1 ispreferably accomplished by using an electronic control or evaluationdevice for the safety switch unit 1. This control or evaluation deviceis therefore provided either in the form of a separate linked unitdirectly on the safety switch unit 1 or the electronic control orevaluation device 2 is disposed externally to the safety switch unit 1.In particular, the control or evaluation unit 3 may also be provided asa part of the control electronics of a handheld device or any otherelectronic machine control system.

Irrespective of whether the safety switch unit 1 is of a double-actionor multi-action design, it is of a multi-channel or multi-circuitdesign, so that if one electric circuit fails, at least one otherelectric circuit remains operational and will continue to assume therespective functions, thereby guaranteeing a high probability that thesafety switch unit 1 will not suffer a total failure. The safety switchunit 1 can therefore be classed as falling within the category known as“failsafe” switch elements, the functional reliability of which issignificantly higher than that of conventional switch elements. Thesafety switch unit 1 preferably has two separate electric switchcircuits 4, 5, each of which is independent of the other, and eachelectric switch circuit 4 and 5 has a separate mechanical operatingelement 6, 7. In particular, the operating element 6 co-operates withthe first switch circuit 4. This being the case, the switch circuit 4 isdesigned to detect the respective position of the displaceable operatingelement 6 and to forward corresponding information or control commandsto the control or evaluation device. The second switch circuit 5co-operates with the other operating element 7 and is likewise designedto generate appropriate signals or control commands for the control orevaluation device depending on the position of the operating element 7.The safety switch unit 1 therefore constitutes a full dual-circuitsystem, both from an electrical and a mechanical point of view. Inparticular, this design offers both a mechanical and an electricalredundancy for the safety switch unit 1.

The two operating elements 6, 7 are mounted on a dimensionally stablemounting frame 8 or in an appropriate support element. The importantpoint is that the two operating elements 6, 7 can be rotatably displacedor pivotably displaced to a limited degree by means of two separatepivot bearings 9, 10 for each operating element 6, 7. These pivotbearings 9, 10 on the mounting frame 8 thus form two pivot axes 11, 12extending transversely to the longitudinal extension of the bar-typeoperating elements 6, 7. The push button unit 2 is disposed in front ofthe two operating elements 6, 7, by reference to an operatingdirection—arrow 13—of the safety switch unit 1.

The push button unit 2 is therefore connected to the two pivotablymounted operating elements 6, 7 so as to guarantee and produce asubstantially translating or linear operating motion of the safetyswitch unit 1. This linear or translating operating motion of the safetyswitch unit 1 is effected starting from the inactive position in thedirection of arrow 13 into the authorisation position and optionallyinto a panic or emergency stop position. If the push button unit 2 ismoved in a straight line relative to the mounting frame 8 as indicatedby arrow 13, the operating elements 6, 7 are pivoted about the pivotaxes 11, 12 thus changing their operating states, in particular thecontact states of the two electric switch circuits 4, 5. Each switchcircuit 4, 5 preferably has at least one electric switch element 14, 15.These switch elements 14, 15 are preferably provided in the form ofswitch contacts, which may be of a standard type. The switch circuits 4,5 each have at least one electric normally open contact 16, 17.Especially if the safety switch unit 1 is of a three-stage design withan emergency stop or panic function, each switch circuit 4,5 is providedwith at least one respective electric normally closed contact 18, 19.These normally closed contacts 18, 19 are operated specifically when thethird switch position of the safety switch unit 1 or push button unit 2is assumed, thus enabling the control or evaluation system 3 to detectan emergency stop or panic situation. The normally closed contacts 18,19 may alternatively or also directly intervene in a switch circuit tobe protected and halt the respective machine functions or machinemovements or initiate other safety measures, such as an emergencyshut-down, for example.

The normally open contacts 16, 17 are operated when the second switchposition or authorisation position is assumed, in particular when theyare switched to the closed contact state. This active contact state ofthe normally open contacts 16, 17 is detected by the control orevaluation device, after which appropriate actions are initiated. Inparticular, the control elements of the machine control system to beprotected are functionally released for normal use.

The switch elements 14, 15 are preferably provided in the form ofelectromechanical switch contacts. Alternatively, the switch elements14, 15 could also be provided as inductive, capacitive, optical ormagnetic detection elements or detection elements operating on someother physical principle.

The switch elements 14, 15 are preferably provided in the form ofstandard, commercially available electromechanical switch elements 14,15 designed for printed circuit board mounting. The spring means neededfor re-setting the normally closed contacts 18, 19 and normally opencontacts 16, 17 are already provided in the interior of these componentsor switch elements 14, 15 and no additional spring or re-setting meansare needed to construct the safety switch unit 1. Using nothing morethan the existing re-setting means in the standard components or switchelements 14, 15, the safety switch unit 1 is constructed so that theyare reliably returned to the initial or inactive position when theoperating forces applied by a user to the push button unit 2 arereleased. One of the reasons for this high functional reliability is thepivot bearings 9, 10 used for the operating elements 6, 7, which areparticularly effective in preventing misalignment and guaranteelong-term functional safety. The fact that no additional spring orre-setting means are needed for the operating elements 6, 7 or for thepush button unit 2 of the proposed safety switch unit 1 significantlyenhances mechanical operating reliability still further. The switchelements 14, 15, available as standard components, have been widelytried and tested and such commercially available components willguarantee functional reliability for thousands of operating cycles.

It is preferable if the operating force which has to be applied in orderto displace or switch the normally closed contacts 18, 19 is greaterthan the operating forces necessary to switch the normally open contacts16, 17. This will result in a clearly perceptible difference between theswitch positions of the safety switch unit 2, 3. Furthermore, the sum ofthe operating forces to be applied to the normally open contacts 16, 17and the normally closed contacts 18, 19 in each switch circuit 4, 5 issuch that the displacement force needed to switch the safety switch unitinto the third switch mode or panic position rises by a step. Theclearly perceptible pressure point between the second switch position(confirmation position) and the third switch position (panic position)significantly facilitates manipulation of the safety switch unit 1,virtually ruling out faulty or incorrect control of the safety switchunit 1.

The mechanical structure and kinematic design of the safety switch unit1 described above ensures that the push button unit 2 is displaced in asstraight a line as possible, even if operating force is applied at anangle or off-centre. The described mechanical design also ensures thatthe respective switch elements 14, 15 of each switch circuit 4, 5 areoperated as far as possible simultaneously and conforming to the sameshape. If the control or evaluation device detects that the signals ofthe respective identical switch elements 14; 15 in the two switchcircuits 4, 5 follow one after the other in time or there is too long atime lag, it can be concluded that the function of the safety switchunit 1 is impaired and an appropriate warning signal can be issued underthe control of the control or evaluation device 3. Likewise insituations where only a single signal can be generated or received bythe two parallel switch circuits 4 and 5, an appropriate alert orwarning signal can be output by the control or evaluation device 3.Optical and/or acoustic output elements may be used for signallingpurposes. To implement acoustic signalling, a summer or similar may beprovided, either directly on the safety switch unit 1 or alternativelyconnected to the central control or evaluation unit.

As may best be seen from FIG. 3, the push button unit 2 and the bearingpoints and displacement clearances for the mechanical components of thesafety switch unit 1 are surrounded or covered by an elasticallyresilient, deformable cover element 42. The cover element 42 ispreferably provided in the form of a rubber membrane 43, which boundsthe operating elements 6, 7 and the push button unit 2 relative to thesurrounding region and prevents ingress by foreign bodies and moisture.The soft-elastic, resilient cover element 42 with the push button unit 2and/or the mounting frame 8 disposed behind or underneath it forms apart-section of the external surfaces of the housing in which the safetyswitch unit 1 is integrated. A housing of this type may be designed as aso-called handheld device or may be a stationary control desk formachines or robots. The safety switch unit 1 is particularly suitablefor mounting in a casing or end region of a portable housing withintegrated display and control elements. In particular, the safetyswitch unit 1 may be inserted in an opening or orifice of such ahousing, in which case the elastic cover element 42 for the mechanicalcomponents of the safety switch unit 1 simultaneously serves as a sealfor the housing in the region of the orifice, dividing it from thesurrounding area. In particular, the rubber-like cover element 42extends as far as the region of a mounting or retaining flange 44(FIG. 1) used to secure the safety switch unit 1 in the interior of anappropriate housing. When the safety switch unit 1 is secured in ahousing, the cover element 42 is therefore firmly clamped between theretaining flange 44 and the internal surfaces of the housing andtherefore provides a dust-proof and liquid-tight screen for the orificeso that the safety switch unit 1 is sealed from the surrounding area ofthe housing once it is inserted. Consequently, no additional seals oradhesive are necessary because the opening from which the push buttonunit 2 is operated in the housing is already sealed by means of thesoft-elastic rubber-like cover element 42. The important factor is thatthe rubber membrane 43 also forms a part-region of the external surfacesin the gripping or holding region of the corresponding housingaccommodating the control electronics.

The control or evaluation device is designed in such a way that acontrol or switch signal indicating the same function must always bereceived from each switch circuit 4, 5. Should it suddenly happen thatonly one switch signal can be received, in particular only oneconfirmation signal or only one emergency stop signal, the control orevaluation device is able to conclude from this that the safety switchunit 1 is damaged or faulty, whereupon appropriate measures can beinitiated, for example warning or error signals issued and/or a safetyshut-down operated.

The two operating elements 6, 7 are mounted so as to pivot relative to amounting frame 8 for at least one electric switch element 14, 15 of thetwo switch circuits 4, 5. In particular, each operating element 6, 7 hasa respective pivot axis 11, 12, with two mutually independent pivotbearings 9, 10 for the two operating elements 6, 7. The two operatingelements 6, 7 are displaceable in rotation to a limited degree via thetwo pivot bearings 9, 10 relative to the mounting frame 8 and theelectric switch elements 14, 15. As illustrated most clearly in FIG. 3,the push button unit 2 is disposed in front of the two operatingelements 6, 7, by reference to the operating direction—arrow 13—therebyenabling a substantially translating or linear operating motion of thesafety switch unit 1 in the direction of arrow 13.

The push button unit 2 disposed in front of the operating elements 6, 7is formed by a part-region of the elastically flexible cover element 42,indicated by broken lines in FIG. 3. In particular, the cover element 42is of a plate-shaped or block-shaped design in the region overlappingthe region where force is applied to the operating elements 6, 7 and thecover element 42 is of a higher stiffness or dimensional stability inthe region where force is applied to the operating elements 6, 7 andoptionally has a reduced coefficient of friction. The push button unit2, which is preferably a rubber part integral with the cover element 42in the form of a bellows with certain thicker regions, is preferablysupported respectively on at least one projection of the operatingelements 6, 7. These projections are shaped so that the operatingelements 6, 7 have a lower friction than the underside of the pushbutton unit 2 and can pivot relative to the cover element 42accordingly. A linear displacement of the push button unit 2 asindicated by arrow 13 will therefore result in a rotating or pivotingmotion of the operating elements 6, 7, thereby causing the electricswitch elements 14, 15 to be switched or displaced by means of thepivoting motion.

The mounting frame 8 on which the operating elements 6, 7 are pivotablymounted by means of the pivot bearings 9, 10 is of a trough-type orbox-type shape in this embodiment. This being the case, the twooperating elements 6, 7 on either side of the mounting frame 8constitute articulated flaps or cover elements which bound the mountingframe 8 at the top, as may best be seen from FIGS. 1 and 3. In addition,as may be seen from FIG. 4, the mounting frame 8 is substantiallyC-shaped in cross section and consists of a substantially flat baseplate 49 from which legs 50, 51 at the oppositely lying side edgesextend out substantially at a right angle to the base plate 49. Thepivot bearings 9, 10 for the operating elements 6. 7 are disposed in thecorner regions of the two legs 50, 51 remote from the base plate 49.

Disposed on the legs 50, 51 or alternatively on the base plate 49 is atleast one retaining tab 52 for securing the safety switch unit 1 in theinterior of a portable housing, for example for an electronic handhelddevice.

As best illustrated in FIG. 3, all electromechanical switch elements 14,15 with the respective electrical switch contacts are disposed on acommon printed circuit board 2. In particular. The first switch circuit4 has a normally open contact 16 and a normally closed contact 18. Thesecond switch circuit 5 likewise has a normally open contact 17 and anormally closed contact 19. The operating element 6 is provided as ameans of displacing or switching the electric switch elements 14 of thefirst switch circuit 4 and the operating element 7 is provided as ameans of switching or displacing the switch elements 15 of the secondswitch circuit 5.

The printed circuit board 22 with the electric switch elements 14, 15 isinserted and retained in position in the substantially C-shaped mountingframe 8 substantially without any clearance. In particular, a bottomface 53 of the printed circuit board 22 is supported as far as possibleby its full surface on an opposing face 54 of the mounting frame 8 andon the base plate 49. The printed circuit board 22 together with theswitch elements 14, 15 soldered thereto is therefore at least partiallyaccommodated in the trough-shaped or housing-shaped mounting frame 8 andpositioned in the mounting frame 8 by means of the legs 50, 51 andoptionally additional webs. The printed circuit board 22 incorporatingthe switch elements 14, 15 can be easily inserted in the cage-typemounting frame 8 by moving the operating elements 6, 7 to the outwardlypivoted position or with the operating elements 6, 7 alreadyaccommodated in the mounting frame 8.

One advantage of this embodiment resides in the fact that theelectromechanical switch elements 14, 15 can be accommodated andretained in the mounting frame 8 without any screw fittings. Inpractical terms, as soon as the printed circuit board 22 incorporatingthe switch elements 14, 15 is placed in the mounting frame 8, theoperating elements 6, 7 can be pivoted into the initial or inactiveposition illustrated in FIG. 3, thereby preventing the switch elements14, 15 or the entire printed circuit board 22 from falling out of themounting frame 8.

To improve the way in which the switch elements 14, 15 are fixed andsecured, flexible, resiliently elastic catch elements 55 are provided onthe mounting frame 8, which secure the printed circuit board 22 relativeto the mounting frame 8. These catch elements 55 thus form a sort ofsnap-fit connection between the printed circuit board 22 and themounting frame 8, thereby enabling the safety switch unit 1 to beassembled without the need for tools. In particular, the printed circuitboard 22 merely has to be slotted into the trough-shaped or housing-typemounting frame 8, without involving any screwing, and is secured readyfor use.

As may be seen from FIG. 1, the mutually remote end regions 30, 31 ofthe two operating elements 6, 7 are respectively mounted so that theycan be pivoted about the separate pivot axes 11, 12. The mutually facingends 26, 27 of the operating elements 6, 7 merge with one another orengage with one another. In particular, the mutually facing ends 26, 27of the two operating elements 6, 7 engage in a meshing arrangement withone another. This mutual meshing engagement is such that the twooperating elements 6 and 7 are not joined to one another in displacementand can still be pivoted independently of one another. The requisitesimultaneous displacement of the two operating elements 6, 7 is obtaineddue to the push button unit 2 as explained above, which is provided as acentral portion of the cover element 42 disposed in front in the mannerdescribed above. The operating elements 6, 7 form operating surfaces 56,57 in the transition region where they merge. These operating surfaces56, 57 constitute a force-introducing zone 58 for the push button unit 2disposed in front with respect to the operating direction—arrow 13. Inorder to improve rolling or sliding behaviour between the push buttonunit 2 and the operating elements 6, 7 to which force is applied, theoperating elements 6, 7 have cambered, in particular convexly curvedprojections in the force-introduction zone 58. In particular, theoperating elements 6, 7 have cam-type raised areas in the region of theforce-introduction zone 58 to which the finger pressure of the user istransmitted via the interposed push button unit 2.

In this embodiment, therefore, the push button unit 2 is formed directlyby the elastically resilient, deformable cover element 42, in particularin the form of a rubber membrane 43. This rubber membrane 43 preferablyalso fulfils the function of sealing off a housing orifice in which thesafety switch unit 1 is inserted and operated with respect to thesurrounding area of an appropriate housing.

As illustrated most clearly in FIGS. 1 and 2, the two operating elements6, 7 are exactly the same and are identical parts. The operating element6 is therefore entirely of the same design as the operating element 7,so that only a few different parts are needed to build the safety switchunit 1. These features reduce manufacturing costs and make small andmedium-sized batch production of the safety switch unit 1 relativelyinexpensive.

The four switch elements 14, 15 of the safety switch unit 1 arerespectively arranged offset from one another in two directionsperpendicular with one another by reference to their seating or supportplane 59, which as a rule is the component side of the printed circuitboard 22. In other words, the switch elements 14, 15, in particular thetwo normally open contacts 16, 17 and the two normally closed contacts18, 19 are disposed at the comers of an imaginary parallelogram. Lookingdown from above onto the seating or support plane 59, which is alignedsubstantially parallel with the base plate 49, the switch elements 14,15 therefore constitute the comers or contour of a virtualparallelogram. This special layout of the switch elements 14, 15 enablesidentical parts to be used for the operating elements 6, 7, therebyreducing the manufacturing costs of the safety switch unit 1 withoutjeopardising quality or reliability.

The switch elements 14, 15 incorporating the normally open contacts 16,17 are also disposed at a shorter distance 39, 40 from the respectivepivot axis 11, 12 of the co-operating operating element 6, 7 than therespective normally closed contact 18, 19 in the same respective switchcircuit 4, 5. In particular, the normally closed contacts 18, 19 arecloser to the middle region between the pivot axes 11, 12 than the twonormally open contacts 16, 17, as illustrated most clearly in FIG. 6. Asa result of the differing lever action of the operating elements 6, 7,starting from the respective pivot axis 11, 12, and the respectivecontact design of the switch elements 14, 15, there is a perceptiblestep in the amount of operating force which has to be applied in orderfor the confirmation position and the panic position to be assumed.

As illustrated most clearly in FIG. 3, operating surfaces 60, 61 of theswitch elements 14, 15 lie substantially within a same plane. In otherwords, the structural height of the normally open contacts 16, 17 may besubstantially the same as the structural height of the normally closedcontacts 18, 19. In order to be able to provide different contact stagesor switch positions with a displacement path disposed in between, theoperating elements 6, 7 may each have a resiliently elastic, flexiblecompensating element 62, 63 co-operating with the switch elements 14, 15incorporating the normally open contacts 16, 17. This compensatingelement 62, 63 is a sort of resiliently mounted tongue, the retainingforce of which is enough to operate the adjusting element of thenormally open contacts 16, 17. As the operating elements 6, 7 pivotfarther from the second contact stage, the compensating elements 62, 63are deflected out relative to the operating elements 6, 7 permitting afurther pivoting motion of the operating elements 6, 7 into the thirdcontact stage due to the increased force. In particular, the operatingforce acting on the normally open contacts 16, 17 can be limited,thereby preventing the normally open contacts 16, 17 from beingsubjected to excessive strain.

Another essential aspect is the fact that the switch elements 14, 15 aredisposed with the normally closed contacts 18, 19 essentially directlyunderneath the force-introduction zone 58 where the operating elements6, 7 merge with one another.

Another aspect of this embodiment of the safety switch unit 1 is thatthe operating elements 6, 7 can be pushed into the initial or inactiveposition by means of the intrinsic return force of the switch elements14, 15, as illustrated in FIG. 3. Consequently, no additional springmeans which would naturally increase the risk of breakage are necessary.The operating elements 6, 7 are returned to the initial or inactiveposition solely by means of the resilient or return means which exist inthe switch elements 14, 15 in any event, provided no external force isbeing applied in the direction of arrow 13. The signals and switchstates of the two switch circuits 4, 5 are processed and acted onaccordingly by a control or evaluation device, not illustrated, which isdirectly integrated in the safety switch unit 1 or connected as aperipheral device.

For the sake of good order, it should be pointed out that in order toprovide a clearer understanding of the structure of the safety switchunit 1, it and its constituent parts are illustrated to a certain extentout of scale and/or on an enlarged scale and/or on a reduced scale.

1. Safety switch unit (1) for electrically controlled machines for usein combination with the actual control elements of the machine controlsystem in a handheld application or manual operation, with at least oneoperating element (6, 7) which is displaced relative to a mounting frame(8) in accordance with the switching function desired by a user, whichis designed to change the switch status of at least one electric switchelement (14, 15), the safety switch unit (1) having at least one switchposition which is maintained only as long as a sufficiently highoperating force is applied to the displaceable operating elements (6,7), wherein two operating elements (6, 7) for at least one respectiveelectric switch element (14, 15) can be displaced in translation orrotation to a limited degree relative to the mounting frame (8) about arespective pivot axis (11, 12) of two pivot bearings (9, 10) and providea substantially translating or straight operating movement of the safetyswitch unit (1) by means of a push button unit (2) which is disposed infront of the two operating elements (6, 7) by reference to the operatingdirection—arrow (13)—of the safety switch unit (1), each of the twooperating elements being mounted to pivot on the respective pivot axisat their remote end regions (30, 31), and their facing ends engaging oroverlapping.
 2. Safety switch unit as claimed in claim 1, wherein theswitch elements (14, 15) are conductively connected to an electroniccontrol or evaluation device (3).
 3. Safety switch unit as claimed inclaim 1, wherein a bottom face (53) of a printed circuit board (22) forall switch elements (14, 15) or a bottom face of the switch elements(14, 15) is supported as far as possible by its full surface on anopposing face (54) of the mounting frame (8).
 4. Safety switch unit asclaimed in claim 3, wherein the printed circuit board (22) is insertedin the housing-type mounting frame (8) without screws.
 5. Safety switchunit as claimed in claim 1, wherein the mutually facing ends (26, 27) ofthe two operating elements (6, 7) overlap with one another in a meshingarrangement but are not linked to one another in displacement and canstill be pivoted independently of one another.
 6. Safety switch unit asclaimed in claim 1, wherein mutually merging operating surfaces (56, 57)of the two operating elements (6, 7) form a force-introduction zone (58)for the push button unit (2).
 7. Safety switch unit as claimed in claim6, wherein the operating elements (6, 7) are upwardly cambered or curvedin a cam-type design in their common force introduction zone (58). 8.Safety switch unit as claimed in claim 1, wherein the elasticallyflexible cover element (42) is plate-shaped or block-shaped in theregion congruent with the zone (58) via which force is transmitted tothe operating elements (6, 7) and is stiffer than the peripheral zoneslying around it.
 9. Safety switch unit as claimed in claim 1, whereinoperating surfaces (60, 61) of the switch elements (14, 15) lie in asubstantially common plane and the two operating elements (60, 61) eachhave a resiliently elastic, flexible compensating element (62, 63)co-operating with the switch elements (14; 15) incorporating thenormally open contact (16, 17).